I agree with Nirvanix. I collimated my 180mm mak (Orion version) two nights ago using Polaris. It took me quite a while to figure out the push-pull procedure (I'm a pretty patient guy), but I now have good collimation. Not great yet, but very good. I'll tweak it some more when I have a chance.
Once I figured out whether to loosen the big or small screw to get the circles to move in the direction I needed, it was much easier. You want to move the image in the direction of the thinner lines, as this will make them thicker. You can also see it as moving the darker middle circular area toward the center, thus 'unsquishing' that squished area. If the rings are squished toward the bottom right, for example, you can see it as the middle of the circle needing to be moved toward the upper left.
1. I used an 11mm 82-deg EP straight through to Polaris (no diagonal).
2. Defocused to see the rings clearly and where they were "squished". If I didn't see the rings clearly, I defocused the other way.
3. The rings were squished at the bottom right of what I saw, so I used the push-pull screws that were toward the bottom right of the rear of the scope (relative to how I had the scope mounted).
4. I loosened either the 4mm or 2.5mm screw and saw if it moved the squished lines toward the edge of the field of view. If not, I retightened and loosened the other one.
5. After I loosened one and the star moved, I recentered the star. I kept doing this until the rings were not squished on that side. I kept recentering the star after every turn of the screw.
6. When the circles were no longer squished on that side, I tightened the other screw (of the push-pull pair) lightly until the mirror position was secure, recentering the star as needed.
7. I repeated in the other directions with the other push-pull screws.
8. When done and the rings were concentric, I defocused in the other direction to see if the circle was symmetrical. One part was thicker than the other, so I collimated it the same way.
The problem I had with Polaris is that there is a companion star that made it seem there was flaring in one direction. I will use another star when I have a chance.
One other thing I noticed that helped me was that while collimating, I saw that one part of the circled seemed a little brighter than the opposite part even though the circles were concentric. I found that the circle needs to be consistently the same brightness all around to be collimated well. In other words, just getting the rings symmetrical is not enough. The brightness must also be symmetrical. I played around with the push-pull to get the brightness consistent.
Hope this helps.